50th Annual Meeting of the American Society of Clinical Oncology (ASCO):
Age, Stage Influence Survival Outcomes in Thyroid Cancer
In patients with thyroid cancer, the likelihood of continued survival as time passes since the diagnosis varies based on several factors, including age, disease stage, and how long the patient has already survived.
These results from a database analyses were presented by Daniel Muenz, MS on June 2, 2014, at the Annual Meeting of the American Society of Clinical Oncology in Chicago, Illinois.
Thyroid Cancer Survival
It is generally considered that the longer patients survive after a cancer diagnosis, the more likely they are to continue to survive. However, the extent to which life expectancy changes as time passes since a diagnosis of thyroid cancer is not well understood. Moreover, most survival analyses do not account for the potential changes in prognosis over time, as they measure an interval of time starting from a discrete point in time and ending at the time of death.
Conditional Survival Outcomes
To evaluate how life expectancy changes as time passes since diagnosis, Mr. Muenz and his colleagues at the University of Michigan, Ann Arbor, evaluated conditional survival outcomes in a large cohort of patients with thyroid cancer, a type of analysis that continually updates survival estimates according to how much time has passed since the diagnosis. The analysis used disease-specific survival as an outcome to evaluate the likelihood of dying from the cancer itself rather than other causes.
Outcomes among 43,392 patients in the Surveillance, Epidemiology, and End Results (SEER) database with well-differentiated thyroid cancer diagnosed between 1998 and 2005 were included in the analysis. The majority of patients (63%) had localized disease; 33.5% had regional disease and 3.7% had distant disease. Patient demographics varied by stage; patients with distant disease tended to be older than patients with localized disease. Males accounted for 20% of localized cases, 28% of regional cases, and 42% of distant cases. After a median follow-up of 6-7 years, rates of death due to thyroid cancer were 0.5%, 3.6%, and 29.5%, in patients with localized, regional, and distant thyroid cancer, respectively.
Across thyroid cancer disease stages, an age effect for disease-specific survival was noted, with older patients having a less favorable prognosis. The hazard ratio for disease-specific survival in patients aged 70-79 years versus those younger than 30 years was 26.6 (95% confidence interval [CI], 8.08-164) for local disease, 59.4 (95% CI, 30.1-140) for regional disease, and 54.5 (95% CI, 20.7-221) for distant disease.
For patients with localized thyroid cancer, 5-year survival outcomes were “excellent”, the researchers reported, both at the time of diagnosis and in subsequent years. For patients with regional thyroid cancer, conditional survival varied by age. In younger patients, survival rates remained high. In older patients, survival rates increased for the first several years then began to decline gradually as the time since diagnosis increased.
For patients with distant thyroid cancer, 5-year survival rates were lowest at diagnosis and gradually improved over time. This finding of improved prognosis over time in patients with distant disease “corroborates the story that as patients survive, their probability of dying from cancer decreases,” the authors concluded.
They added that understanding these survival rates may assists patients and physicians in the treatment planning process.